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Occupational Medicine Advance Access originally published online on July 26, 2007
Occupational Medicine 2007 57(7):512-517; doi:10.1093/occmed/kqm076
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© The Author 2007. Published by Oxford University Press on behalf of the Society of Occupational Medicine. All rights reserved. For Permissions, please email: journals.permissions@oxfordjournals.org

Assessment of the hand–arm vibration syndrome: thermometry, plethysmography and the Stockholm Workshop Scale

Aaron Thompson, Ron House and Michael Manno

Department of Occupational and Environmental Health, St Michael's Hospital, Toronto, Ontario, Canada

Correspondence to: Aaron Thompson, Occupational Health Services Program, St Michael's Hospital, 61 Queen Street East, 8th Floor, Toronto, Ontario, Canada M5B 1W8. Tel: +416 426 9174; e-mail: aaron.thompson{at}utoronto.ca


   Abstract
Top
 Abstract
Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
 References
 
Background The Stockholm Workshop Scale (SWS) provides a staging scheme for hand–arm vibration syndrome (HAVS) based on subjective history. Cold provocation finger thermometry and plethysmography are commonly used objective tests for the vascular component of HAVS.

Aim To examine the correlation between the cold provocation tests and SWS vascular stage. A secondary goal was to evaluate the correlation between cold provocation finger plethysmography and thermometry testing.

Methods Patients investigated for HAVS at St Michael's Hospital, Toronto, Ontario, were subjected to the same protocol including a questionnaire, clinical assessment and objective testing. Spearman correlation coefficients were calculated for the vascular tests with the SWS and for the vascular tests themselves. Logistic regression models controlled for age, smoking, use of vasoactive medications and time since last vibration exposure.

Results One hundred and thirty-nine patients investigated for HAVS consented to participate in the study. The correlation coefficients for plethysmography ({rho} = 0.14) and thermometry ({rho} = 0.18) with the SWS were not statistically significant. Plethysmography and thermometry results were significantly correlated ({rho} = 0.47, P < 0.001). Logistic regression showed plethysmography and thermometry to weakly predict SWS vascular stage (OR 1.5 and 1.3, respectively). None of the potential confounders had a significant effect in the models.

Conclusion The results of plethysmography and thermometry did not significantly correlate with SWS vascular stage in this study. The objective tests did correlate with each other, suggesting that they are reliable measures of similar phenomena likely related to underlying vascular pathology.

Keywords      Cold provocation tests; hand–arm vibration syndrome; photocell plethysmography; Stockholm Workshop Scale; thermometry


   Introduction
Top
 Abstract
 Introduction
Methods
 Results
 Discussion
 Conflicts of interest
 References
 
Hand–arm vibration syndrome (HAVS) is a recognized occupational disorder manifesting as vascular, neurological and/or musculoskeletal symptoms in the upper limb arising after exposure to hand-transmitted vibration [1–3]. The Stockholm Workshop Scale (SWS) for the vascular component is a staging scheme that is based on the patient's subjective history. The SWS has been widely used in clinical work and epidemiological studies [4–6]. Though not intended to serve as a ‘gold standard’ test, the SWS is often used as a reference criterion for investigating the diagnostic utility of objective tests for HAVS [2,5–13]. The subjective nature of the SWS makes it less than ideal for use as either a diagnostic tool or reference criterion.

Finger skin temperature (FST) is a physiological parameter used for evaluating the degree of cold-induced vasoconstriction in the digital vessels, with a delay in rewarming signifying persistent digital vasospasm [14,15]. Past studies have found poor correlation between the SWS and cold provocation FST testing [11,14,16–20].

Cold provocation testing using photocell plethysmography has been described in the literature [21–23]. Interpretation of the tracings from photocell plethysmography considers changes in pulse amplitude as an indicator of the degree of vasospasm [15], while tracing shape provides evidence of vascular abnormality [24]. Similar to cold provocation FST tests, finger photocell plethysmography has been found to correlate poorly with the SWS [22,25].

The results of photocell plethysmography and FST recovery have been found to correlate well [14], though these results have been questioned due to small sample size [6].

This study focuses on the vascular component of HAVS to add to the existing literature examining the use of FST recovery and finger photocell plethysmography in the diagnosis of HAVS.


   Methods
Top
 Abstract
 Introduction
 Methods
Results
 Discussion
 Conflicts of interest
 References
 
The study population consisted of 139 patients investigated for HAVS at St Michael's Hospital, Toronto, Ontario. Each patient was subjected to the same protocol consisting of a questionnaire, clinical assessment and objective testing. Subjects were not asked to restrict smoking or use of caffeine prior to testing, though smoking status and time since last vibration exposure were recorded. For each subject, testing was conducted on the same day, thus eliminating temporal variation in symptoms and reporting. All examinations were conducted by one of two occupational medicine physicians. Thermometry and plethysmography were conducted at two sites that were blinded to each other and to the SWS results.

The protocol required each patient to first complete a questionnaire detailing his/her history of symptoms and hand–arm vibration exposure. One of two physicians then obtained a detailed and standardized medical history, including the history of HAVS symptoms, and conducted an examination of the vascular, neurological and musculoskeletal status of the upper extremities. On completion of the assessment, the physician assigned the patient a Stockholm stage based on the patient's symptomatology.

A vascular technician carried out the photocell plethysmography. Baseline tracings for all digits of both hands were obtained at an ambient room temperature between 21 and 24°C. Both hands were then immersed in 10°C water for 2 min. The photocell plethysmography test was then repeated and the tracings were interpreted by comparing the post-immersion results to the measured baseline amplitudes. The tracings were interpreted as showing no abnormality before and after cold stress or some degree of abnormality graded as mild, moderate or severe according to standardized values for changes in amplitude.

The cold provocation FST protocol used a thermocoupler attached to the tip of each digit to record skin temperatures. Baseline values were obtained over a period of 2 min prior to immersion. The hands were then immersed in 10°C water. A sphygmomanometer was inflated around each of the patient's wrists for the initial 5 min of immersion. The sphygmomanometer was then deflated and the hands were kept immersed for a further 2 min. The skin temperatures of the digits were recorded throughout the 7-min immersion period. Readings were then recorded during the rewarming period for a further 7 min following immersion. In a normal subject, after the sphygmomanometer cuff is released, there is a reactive hyperemia during immersion followed by a rapid recovery once the hands are removed from the cold water bath. The parameters used to assess rewarming were the finger temperatures at 3 and 7 min after cold stress as described by Pelmear et al. [26,27]. Cold-induced vasospasm was diagnosed when a prolonged recovery phase was recorded.

The data presented in this paper were obtained from a study approved by the Ethics Review Committee of St Michael's Hospital, a tertiary care hospital affiliated with the University of Toronto.

Spearman correlation coefficients were calculated to investigate the correlation between each of the vascular tests and the SWS as well as the correlation between the vascular tests themselves.

Logistic regression models of SWS were constructed to control for age, smoking, use of vasoactive medications and time since last vibration exposure. Age and time since last vibration exposure were included in the models as continuous covariates. Smoking and use of vasoactive medications were included in the models as dichotomous covariates. A P-value of <0.05 was considered to be statistically significant. The models were run separately for thermometry and plethysmography due to concern regarding collinearity of the variables.

All statistical analyses were performed using SAS, version 8.0 (SAS Institute Inc., Cary, NC).


   Results
Top
 Abstract
 Introduction
 Methods
 Results
Discussion
 Conflicts of interest
 References
 
One hundred and thirty-nine of 141 consecutive patients referred to our clinic for assessment of HAVS consented to participate in the study. All patients had a history of vibration exposure and presented with symptoms consistent with some component of HAVS.

The demographic results of the study subjects showed them to be characteristic of the vibration-exposed trades (Table 1). The overwhelming majority of participants were male, with 134 males and only 5 females. The majority of subjects were between 40 and 60 years old, with 33 (24%) being 20–39 years old, 43 (31%) being 40–50 years old, 42 (30%) being 50–59 years old and only 21 (15%) being over 60 years old. Forty-eight participants were current smokers (35%) and 38 were on vasoactive medication. The mean length of vibration exposure among the subjects was 23.9 years (SD = 11.3, range 0.5–47).


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  		Table 1. Characteristics of study population

 
The SWS reading for the dominant hand was considered for each patient (Table 2). The majority of cases were SWS vascular Stage 3 (45%), followed by Stage 2 (25%) and Stage 1 (16%), and 14% were vascular Stage 0. There was one subject with trophic changes in the fingers (SWS vascular Stage 4). The distribution of thermometry results showed the majority of patients to have severe abnormalities (54%), while the distribution of plethysmography results showed the majority of patients to have moderate abnormalities (54%).


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  		Table 2. Distribution of vascular, thermometry and plethysmography stages

 
Spearman correlation coefficients were calculated to investigate the correlation between each of the vascular tests and the SWS (Table 3). Neither the correlation coefficient for plethysmography ({rho} = 0.14) or for thermometry ({rho} = 0.18) with the SWS was statistically significant. Plethysmography and thermometry were found to be significantly correlated with a Spearman correlational coefficient of {rho} = 0.47 (P < 0.001).


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  		Table 3. Spearman correlation coefficients among the vascular tests and the SWS

 
Logistic regression models were constructed using the SWS vascular score as the outcome variable (Tables 4 and 5). Thermometry, plethysmography, age, smoking, use of vasoactive medications and time since last vibration exposure were used as the independent variables. Models were run separately using either thermometry or plethysmography. Increased scores on thermometry (OR 1.35, 95% CI 1.00–1.81) and plethysmography (OR 1.50, 95% CI 1.01–2.21) were found to significantly increase the odds of having an increased SWS score. None of the potential confounders of age, smoking status, use of vasoactive medications or time since last vibration exposure had a significant effect in the models.


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  		Table 4. Polytomous regression model for SWS versus thermometry

 

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  		Table 5. Polytomous regression model for SWS versus plethysmography

 

   Discussion
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
Conflicts of interest
 References
 
The principal finding of this study was that although the cold provocation tests using FST recovery and finger photocell plethysmography did not significantly correlate with the SWS vascular stage, the two vascular tests did significantly correlate with each other. The findings of this study are consistent with the literature, which suggests that digital photocell plethysmography and cold provocation digital thermometry correlate poorly with the SWS vascular stage [11,14,28–31].

This study's methodological strengths included a relatively large sample size, attention to blinding in the measurements being compared and the fact that the tests and clinical SWS ratings were done on the same day, thus helping to eliminate sources of variability. The study considered the correlation between the vascular tests themselves, which few studies have analyzed. Bovenzi examined 20 men with documented HAVS and 64 vibration-exposed men without symptoms, and reported good correlation between cold provocation tests using FST and finger systolic pressure measurements (r = 0.42, P < 0.001) [14]. This study reproduces this finding with the added strength of a larger sample size.

A limitation of this study was that it did not address the problem of the repeatability or reproducibility of the objective tests [32,33]. A second limitation was that no restrictions on smoking or caffeine use were placed on subjects prior to testing. The effects of smoking and caffeine use prior to testing would likely result in non-differential misclassification with underestimation of the correlation coefficients. In our study, acute effects related to caffeine use and/or smoking would be small because smoking was not found to be associated with either test or the SWS, and the vascular tests were not started until the worker had been in the clinic for at least 1 h. During this period, coffee was not consumed and smoking was not allowed.

The finding that cold provocation tests measuring FST and finger plethysmography measurements are significantly correlated suggests that the objective vascular tests are measuring similar phenomena likely related to underlying vascular pathology. That the two procedures do not correlate to a greater extent may reflect the fact that they are measuring two distinct aspects of vascular response, the induction of vasospasm (plethysmography) versus recovery from vasospasm (thermometry).

One can conceptualize that the physiological vascular abnormalities, objective test results and clinical manifestations of hand–arm vibration may be distinct entities that overlap (Figure 1). The vascular abnormalities in hand–arm vibration-exposed individuals extend beyond simple vasospasm and, as such, we cannot expect these tests to be very highly correlated. Subclinical pathophysiological changes are likely to occur in vibration-exposed individuals, and it may be that some individuals do not manifest symptoms despite chronic exposure and early pathological changes. As such, it is understandable that the results of objective testing do not correlate perfectly with clinical symptomatology, and in turn, the SWS.


Figure 1
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  		Figure 1. Venn diagram conceptualizing the overlap of the physiological vascular abnormalities, objective test results and clinical manifestations in HAVS.

 
The fact that the SWS vascular stage does not correlate well with the objective tests demonstrates that the different measures may represent distinct outcomes applicable to specific problems. The nature of the problem thus becomes paramount in deciding which outcome modality to use and how it should best be interpreted. For treatment and management purposes, the examiner may wish to focus on subjective symptoms using the SWS. At the other end of the spectrum, research on hand–arm vibration may wish to focus on determining dose–response curves for vasospastic disease and exposure to vibration frequencies and magnitudes. In this scenario, the researcher may be better served by the more precise and sensitive measurement of vasospastic changes, and recovery from those changes, that plethysmography and thermometry provide [6].

Determining the presence and extent of disease is necessary for decision making in compensation claims. Compensation decisions are usually based on impairment and disability, and as such, clinical manifestations are of paramount importance. A high correlation of the objective tests with pathophysiological changes may result in positive tests in subjects without symptomatic clinical disease. In such cases, compensation boards may wish to select criteria for a positive test that optimizes specificity—for example using higher cutoff points or combining tests using more stringent criteria to reduce the number of false positives.

Future research should focus on methods of testing that address the reproducibility and repeatability of testing techniques. A second research focus should be to define cutoff points for use in comparing the objective tests with subjective symptomatology.


Key points
  1. Cold provocation tests using FST recovery and tests using finger photocell plethysmography significantly correlate with each other but not with the SWS vascular stage.
  2. Objective cold provocation studies may be a more reliable, and potentially more sensitive, measure of vascular pathology than the SWS.
  3. For treatment purposes, the clinician should use the SWS, whereas research on the vascular component of hand–arm vibration may be better served by the use of plethysmography and thermometry.

 


   Conflicts of interest
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
References
 
None declared.


   References
Top
 Abstract
 Introduction
 Methods
 Results
 Discussion
 Conflicts of interest
 References
 

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Re: Thompson A, House R, Manno M. Assessment of the hand-arm vibration syndrome: thermometry, plethysmography and the Stockholm Workshop Scale
Occup. Med., May 1, 2008; 58(3): 223 - 224.
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